Human lung converting enzyme will be further purified by deoxycholate extraction of fresh lung, followed by treatment with CM Sephadex, DEAE chromatography and by affinity chromatography. Lung enzyme units will then be studied with regard to inhibition by the various components of the renin-angiotensin system and the Kallikrein-kinin system. We have determined that both plasma and semi-purified lung converting enzymes are inhibited by angiotensin II, 1-sarc-8-ileu angiotensin II, and tetra- and tridecapeptide renin substrates. The bradykininase activity of these enzymes is aldo substantially inhibited by these fragments. The effect of converting enzyme from lung and plasma in activating tridecapeptide renin substrate to angiotensin III, human renin substrate and tetradecapeptide renin substrate, will also be evaluated.